1. Field of the Invention
The present invention relates to a filament assembly, and more particularly to a filament assembly for a twinkling bulb.
2. Description of Related Art
The electric light bulb has illuminated the world for a century, bringing unimagined advances to our lives. The bulbs may also be used as a decoration for special occasions such as a birthday party or a Christmas party.
With reference to FIG. 3, a conventional twinkling bulb in accordance with the prior art comprises a bulb seat (not shown), a glass shell (90) and a filament assembly. The glass shell is transparent and mounted on the bulb seat. The filament assembly is mounted inside the glass shell on the bulb seat and has two magnesium-plated filaments (91), a glass bead (92), a fuse (93), a tungsten filament (94) and a flexible tongue (95). The magnesium-plated filaments (91) are mounted inside the glass shell (90) on the bulb seat, spaced apart a certain distance and respectively having a top end. The glass bead (92) is mounted to the magnesium-plated filaments (91) and both keeps the magnesium-plated filaments (91) upright and separate form each other. The fuse (93) is mounted around the magnesium-plated filaments (91). The tungsten filament (94) is mounted between the top ends of the magnesium-plated filaments (91). The flexible tongue (95) is mounted on one of the magnesium-plated filaments (91) and has two metal strips, a fixed end and a distal end. The metal strips are joined longitudinally and have different coefficient of thermal expansion. The fixed end is attached to one of the magnesium-plated filaments (91) and the distal end is separate from the other.
When the twinkling bulb is electrified, the current passes through the magnesium-plated filament (91), the fuse (93), the tungsten filament (94) and the flexible tongue (95). The tungsten filament (94) radiates heat and light and causes temperatures of all components inside the glass shell (90) to rise. As the temperature rises, the electrified flexible tongue (95) bends to touch the opposite magnesium-plated filament (91) to cause a short circuit. The tungsten filament (94) fails to radiate heat and light. Then, the temperature of the flexible tongue (95) accordingly falls and the distal end of the flexible tongue (95) separates from the opposite magnesium-plated filament (91) to make the tungsten filament (94) radiate heat and light up again.
The conventional twinkling bulbs can be assembled in series connection or in parallel connection to become a twinkling bulb assembly to be use as a decoration for a Christmas tree or celebratory items. When the bulb assembly is electrified, the bulbs light irregularly. However, the distal end of flexible tongue (95) does not not bend precisely back to the same position every time when the temperature thereof decreases. The distal end might bend to a position lower than a critical position resulting in that the distal end cannot bend again to the touch the opposite magnesium-plated filament and the twinkling function of the twinkling bulb fails. Furthermore, metal fatigue also causes the flexible tongue (95) to fail to bend properly and the twinkling function of the twinkling bulb again fails.
To overcome the shortcomings, the present invention provides a filament assembly for a bulb to mitigate or obviate the aforementioned problems.